Seating depth question

[fairchaser]

So, I determined a great seating depth for my .308. But, when I bought more bullets the ogive was different. Even though it was the exact same bullet, the seating die pushed it in as much as 10,000 different when measured from the ogive.

Should I seat to the overall length or the base to ogive? When I seated to a predetermined jump from the ogive, it seems I lost the magic and I'm thinking I should have kept the overall length constant. But, I don't know.

I guess it depends on what the seating depth actually affects. I did notice this load, was 30 FPS faster on average and not as accurate.

 

[infoman jr.]

Your gun doesn't care where the bullet tip is (although your mag might).

 

[Jcalder]

Base to ogive is what I would do first if they'll fit in the magazine box.


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[Omega]

I take all my measurements from the base to ogive, with a comparator. I use an OAL gauge to get the jump measurement for the particular rifle I am loading for, but my Rem 700 shoots both commercial loads as well as surplus ammo so don't know how much using my method helps.

 

[MUP]

What is the difference of jump to the lands from the original bullet ogive compared to the new box of bullets? Base to ogive of the original loaded round vs the latest round with the new bullets that is. If the ogive is that much different from one box of the same bullets to another, I might consider calling the bullet manufacturer and asking them about it.

 

[fairchaser]

Your gun doesn't care where the bullet tip is (although your mag might).

I agree, the gun doesn't care where the tip is but changing my seating depth does change the cartridge volume and therefore affects the pressure and speeds. I think this is where I'm fighting the battle. To stay consistent base to ogive, I'm having to change the actual seating depth and this is affecting my speeds and even changing the barrel harmonics. I'm wondering that after I've determined the optimal seating depth on my die, to just leave it there even if the ogive changes lot to lot. More testing I guess.

 

[Hardwoodmaterials]

I always measure to the ogive and write that down as my length in my notes. If I open a new box of the same bullet I usually measure a few to see how close they are from base to ogive to the last box. If they are real close I just continue loading to the same ogive depth. You will be surprised how much of a different there will be in the same bullet from box to box with some brands. The overall length only matters if it doesn't fit in the magazine.

If you want to really see some variation just measure the length and weigh the powder charge inside cheap factory ammo like Rem. Corlokts, Federal blue box, Ect. We have all seen rifles shoot cheap ammo under an inch at 100yds but after you tear down a few you will wonder how it could hit the broad side of a barn twice in a row!

 

[fairchaser]

I always measure to the ogive and write that down as my length in my notes. If I open a new box of the same bullet I usually measure a few to see how close they are from base to ogive to the last box. If they are real close I just continue loading to the same ogive depth. You will be surprised how much of a different there will be in the same bullet from box to box with some brands. The overall length only matters if it doesn't fit in the magazine.

If you want to really see some variation just measure the length and weigh the powder charge inside cheap factory ammo like Rem. Corlokts, Federal blue box, Ect. We have all seen rifles shoot cheap ammo under an inch at 100yds but after you tear down a few you will wonder how it could hit the broad side of a barn twice in a row!

I think the key on some of these factory loads is the 100 yard accuracy. If you took those same MOA shots out to 300, you will see much less than MOA results due to variations in speeds etc.

I am finding out now why serious shooters will buy lots of 2000-3000 bullets, powder, primers, etc each time they replace a barrel. It's the only way to control some of these inconsistencies. It's just hard to buy all that at once.

 

[DaveB]

Yep. I don't own a Mr.B-level weapon but I do buy die sets for each rifle. So I have two 2 complete sets for 300 WinMag, 30/06, 7mm08, and 223. And I generally order enough bullets brass and primers to last a very long time even before the rifle is in my hands.


I tried some TGK's recently (no Accubonds/Partitions available) and after truly miserable results I turned testing over to my Sons. After first group Son turns and says "these green tip things are junk".

I am not sure you will find a happy conclusion. I did a count recently and nearly 200 rounds went downrange in our 308 before someone suggested Varget and that did the trick. No other powder will ever be used in that weapon. Horses for courses.

 

[Deer Assassin]

This is why I like buying bullets in bulk of the same lot

 

[fairchaser]

Yep. I don't own a Mr.B-level weapon but I do buy die sets for each rifle. So I have two 2 complete sets for 300 WinMag, 30/06, 7mm08, and 223. And I generally order enough bullets brass and primers to last a very long time even before the rifle is in my hands.


I tried some TGK's recently (no Accubonds/Partitions available) and after truly miserable results I turned testing over to my Sons. After first group Son turns and says "these green tip things are junk".

I am not sure you will find a happy conclusion. I did a count recently and nearly 200 rounds went downrange in our 308 before someone suggested Varget and that did the trick. No other powder will ever be used in that weapon. Horses for courses.

I'm shooting the 168 smk's and they shoot well in my gun behind Varget ( thanks to you) but I need to go heavier for competition. But, I'm well into the midlife of this barrel and don't want to put too many rounds through it to find another load with another powder.

 

[fairchaser]

What is the difference of jump to the lands from the original bullet ogive compared to the new box of bullets? Base to ogive of the original loaded round vs the latest round with the new bullets that is. If the ogive is that much different from one box of the same bullets to another, I might consider calling the bullet manufacturer and asking them about it.

I'm having to seat the new bullet almost 10,000 less to get the same jump to the lands. Some stuff I read online, says this is not unusual. Even the bullet length can vary by that much. Some bullet manufacturers are better than others for consistency. That's why some like to jam their bullets but the bullets I use like to jump. I'm just gonna have to work with what I've got.

 

[MUP]

Are you measuring the bullet itself from it's base to the ogive and getting .010" difference, or are you getting .010" difference when seating them in the case? I'm still a little unsure here. I wouldn't know how to check the actual ogive tangent other than just taking a measurement from the base of the bullet to the ogive itself with a comparator.

 

[fairchaser]

Are you measuring the bullet itself from it's base to the ogive and getting .010" difference, or are you getting .010" difference when seating them in the case? I'm still a little unsure here. I wouldn't know how to check the actual ogive tangent other than just taking a measurement from the base of the bullet to the ogive itself with a comparator.

I haven't measured the bullet itself. But, the distance from the tip to the ogive is what's different. The bullet length may also be different but I don't know since the bullet is already seated in my case. Since the bullet is seated from the tip by the die and measured by the ogive, that's where the problem starts. My die has a micrometer and the reading is different to achieve the same base to ogive measurement. I assume it's also seated longer in the case allowing more case capacity and higher pressures. That's why my FPS jumped by 30. I think that's the reason anyway. I hope that was clear enough.

 

[MUP]

Hmmmm. I have had .003-.005 variations before, but I usually back my die off a round or two on the fine adjustment before I start and adjust the first round and then continue on from there to keep my distance to the lands the same. Interesting.

 

[fairchaser]

Hmmmm. I have had .003-.005 variations before, but I usually back my die off a round or two on the fine adjustment before I start and adjust the first round and then continue on from there to keep my distance to the lands the same. Interesting.

You might not notice small changes unless you have a micrometer built into to your seating die. I know I set my die to a long depth and then check the length with the comparator and keep moving closer to my ideal jump. But one time the die will be on .019 and then on the next lot .009 but stay pretty consistent throughout that box of bullets. If all the bullets are the same length then that .010 translates to more case capacity. From what I've read, since the case is a combustion chamber, pressures can increase causing more FPS. That's the theory anyway.

 

[MUP]

Yes sir, and I concur. I check each length of each round after pressing a bullet in, but once set I rarely have to move the seating stem, maybe .002-.005 as I mentioned. I have my self imposed tolerance of +/- .002" for seating depth, and anything out of that range gets adjusted. I would think, however, that once set, the outcome would be relatively close each time, regardless of bullet length, for OAL distance measured with a comparator. The ogive may indeed be different by you getting a different reading from case to case.